1. Field of the Invention
The present invention relates to a substrate for a liquid crystal display device and a liquid crystal display device which are used as, for example, a display unit of an electronic apparatus.
2. Description of the Related Art
In recent years, liquid crystal display devices have come to be used for TV receivers, monitor devices of personal computers, etc. In these purposes, liquid crystal display devices are required to have a superior viewing angle characteristic that allows the display screen to produce high-quality images even when viewed from all directions. MVA (multi-domain vertical alignment)-type liquid crystal display devices are known as ones capable of providing a superior viewing angle characteristic. In MVA-type liquid crystal display devices, the liquid crystal molecules are aligned perpendicularly to the substrates when no voltages are applied. When voltages are applied to the liquid crystal, the alignment of the liquid crystal molecules is determined by projections formed on the counter substrate or slits formed in a transparent electrode (ITO electrode).
In general, in vertical-alignment-type liquid crystal display devices such as MVA-type ones in which the liquid crystal molecules are aligned perpendicularly to the substrates, a transmittance vs application voltage characteristic (T-V characteristic) obtained when the display screen is viewed from the direction perpendicular to it (i.e., front direction) is different from that obtained when the display screen is viewed from an oblique direction. Because of this phenomenon, even if the T-V characteristic obtained when the display screen is viewed from the direction perpendicular to it is optimized, the color of an image looks whitish due to a distorted T-V characteristic when the display screen is viewed from an oblique direction. A pixel structure for solving this problem is known in which each pixel is divided into two sub-pixels A and B. A pixel electrode α of the sub-pixel A is electrically connected to the source electrode of a thin-film transistor (TFT) for pixel driving and a pixel electrode β of the sub-pixel B is insulated from the source electrode of the TFT and rendered in a floating state.
In this pixel structure, a control capacitance Cc is formed by the pixel electrode β of the sub-pixel B, the source electrode of the TFT, and an insulating film interposed between these two electrodes. Because of capacitive coupling via the control capacitance Cc, a lower voltage is applied to the pixel electrode β of the sub-pixel B than the pixel electrode α of the sub-pixel A. As a result, regions having different T-V characteristics are formed in the two regions of each pixel so as to lower the degree of distortion of T-V characteristics obtained when the display screen is viewed from oblique directions, whereby the phenomenon that an image looks whitish when viewed from an oblique direction can be suppressed and the viewing angle characteristic can be improved.
The above technique is disclosed in JP-A-2-12, U.S. Pat. No. 4,840,460, and Japanese Patent No. 3,076,938.
Incidentally, a slit that is formed between the adjoining end portions of the pixel electrodes α and β and serves to separate the sub-pixels A and B is usually as small as several micrometers in width. Therefore, if a patterning failure occurs in forming the pixel electrodes α and β, a pixel electrode forming material may remain in the slit to short-circuit the pixel electrodes α and β. This is a factor of lowering the production yield of the liquid crystal display device. Further, if the pixel electrodes α and β are short-circuited, the same voltage is applied to the sub-pixels A and B and hence the effect of lowering the degree of distortion of oblique-direction T-V characteristics is lost, resulting in a problem that it becomes difficult to obtain good display characteristics.